Prior Cosmetic Techniques and Their Disadvantages Prior art techniques for modifying the appearance of skin include natural tanning, artificial tanning, and the deliberate application of cosmetics. Each of these prior art techniques has limitations.
Typically, the applications of cosmetic substances to skin are largely manual, for example through the used of brushes, application tubes, pencils, pads, and fingers. These application methods make prior art cosmetics imprecise, labor intensive, expensive, and sometimes harmful, when compared to the computerized techniques of the present invention.
Most prior art cosmetic approaches are based on the application of opaque substances. As explained in the cross-referenced application U.S. Ser. No. 11/503,806, there is a need for the precise computer-controlled application of reflectance modifying agents (RMAs), such as transparent dyes, to provide a more effective modification of appearance. In this specification, the terms “reflectance modifying agent” or “RMA” refer to any compound useful for altering the reflectance of another material, and are explained in further detail below. Some examples of RMA are inks, dyes, pigments, bleaching agents, chemically altering agents, and other substances that can alter the reflectance of human skin and other features. The terms “dye” and “transparent dyes” are used for brevity in this specification to represent any RMA.
Moreover, cosmetics are typically applied manually to make people look more like certain images. For example, cosmetics may be applied to reconstruct the former appearance of people whose features have been altered or damaged. For example, cosmetics may be applied to the skin of patients who have been burned, to make the burned skin appear to have the color and texture it had before the burns. Cosmetics may be used to create the appearance of eyebrows on cancer patients who have lost their hair as a result of chemotherapy or radiation treatment. And cosmetics are used generally to make older people look more like they were when young. In addition, cosmetics may be used to make people look more like any desired model of themselves that they might have.
Typically the models used as the basis for these cosmetic applications are                People's memories of the way they looked previously.        Prior images of people, such as photographs, videos, paintings, drawings, and digital images such as those stored on computers, cell phones, and digital cameras.        Images of people as they would like to be seen, for example in drawings, enhanced photographs, or computer-generated images.        
Ideal models derived from certain people are also used as the basis for cosmetic applications on other people. For example, a makeup artist may create a “look,” consisting of a certain combination of colors, shading contrasts, and even feature shapes, such as eyebrow shapes, that is used as model for cosmetics applied to many different people. Such a look may be based on the appearance of a popular actress, for example a Nicole Kidman look or a Catherine Zeta-Jones look, because many women would like to look like those actresses. Makeup artists can apply cosmetics to make different people all have a similar look, or individuals may apply their own cosmetics to create such effects, for example based on magazine pictures or digital images of actresses.
However, manual techniques of applying cosmetics for such changes based on images, such as digital images, can be time consuming and require considerable skill to be done well, as anyone can attest who has tried to draw on eyebrows for a distressed cancer patient to match a digital image of her.
Therefore, there is a need for the precise application of reflectance modifying agents (RMAs) to provide a more effective, more automated, faster, less expensive, and less dangerous modification of the appearance of skin to cosmetically change people's features based on digital images.